U.S. patent application number 14/566428 was filed with the patent office on 2015-06-11 for inspection appratus and inspection method.
The applicant listed for this patent is OSAKA UNIVERSITY, SCREEN HOLDINGS CO., LTD.. Invention is credited to Akira ITO, Iwao KAWAYAMA, Hidetoshi NAKANISHI, Masayoshi TONOUCHI.
Application Number | 20150162872 14/566428 |
Document ID | / |
Family ID | 53272197 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150162872 |
Kind Code |
A1 |
NAKANISHI; Hidetoshi ; et
al. |
June 11, 2015 |
INSPECTION APPRATUS AND INSPECTION METHOD
Abstract
An inspection apparatus inspects a solar cell. The inspection
apparatus includes: a short-circuiting element that electrically
connects an anode as a p-type semiconductor layer and a cathode as
an n-type semiconductor layer of the solar cell to short-circuit
the solar cell; an irradiation part that irradiates the solar cell
short-circuited by the short-circuiting element with pulse light;
and a detection part that detects an electromagnetic wave emitted
from the solar cell in response to the irradiation of the solar
cell with pulse light from the irradiation part.
Inventors: |
NAKANISHI; Hidetoshi;
(Kyoto-shi, JP) ; ITO; Akira; (Kyoto-shi, JP)
; KAWAYAMA; Iwao; (Osaka, JP) ; TONOUCHI;
Masayoshi; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCREEN HOLDINGS CO., LTD.
OSAKA UNIVERSITY |
Kyoto-shi
Osaka |
|
JP
JP |
|
|
Family ID: |
53272197 |
Appl. No.: |
14/566428 |
Filed: |
December 10, 2014 |
Current U.S.
Class: |
324/761.01 |
Current CPC
Class: |
H02S 50/15 20141201;
G01R 31/2656 20130101 |
International
Class: |
H02S 50/15 20060101
H02S050/15; G01R 31/265 20060101 G01R031/265 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2013 |
JP |
2013-254807 |
Claims
1. An inspection apparatus that inspects an inspection object
including an anode and a cathode, the inspection apparatus
comprising: a short-circuiting element that electrically connects
the anode and the cathode of said inspection object to
short-circuit said inspection object; an irradiation part that
irradiates said inspection object short-circuited by said
short-circuiting element with light; and a detection part that
detects an electromagnetic wave emitted from said inspection object
in response to the irradiation of said inspection object with said
light from said irradiation part.
2. The inspection apparatus according to claim 1, wherein said
anode is a p-type semiconductor and said cathode is an n-type
semiconductor.
3. The inspection apparatus according to claim 1, wherein said
inspection object is a multi-junction type solar cell formed by
stacking a plurality of solar cells having absorption wavelength
regions different from each other.
4. An inspection method for inspecting an inspection object
including an anode and a cathode, the inspection method comprising
the steps of: (a) electrically connecting said anode and said
cathode to short-circuit said inspection object; and (b)
irradiating said inspection object, which is put into the
short-circuit state in said step (a), with light to detect an
electromagnetic wave emitted from said inspection object in
response to the irradiation of said inspection object with the
light.
5. The inspection method according to claim 4, wherein said anode
is a p-type semiconductor and said cathode is an n-type
semiconductor.
6. The inspection method according to claim 4, wherein said
inspection object is a multi-junction type solar cell formed by
stacking a plurality of solar cells having absorption wavelength
regions different from each other.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a technology of inspecting
a semiconductor device, a photo device, or a light emitting
device.
[0003] 2. Description of the Background Art
[0004] Nowadays, a technical development that visualizes dynamic
behaviors such as generation, acceleration, and recombination of
photocarriers (particularly, electrons), what is called carrier
dynamics has been expected in fields of a semiconductor and a photo
device, particularly in the field of a solar cell. An observation
system used in time regions of femtosecond to picosecond is
required in the carrier dynamics.
[0005] There is performed research and development on an
observation system in which an electromagnetic wave (terahertz
wave, 10.sup.12Hz) in a terahertz region is used. The
electromagnetic wave in the terahertz region has high
transmissivity like a radio wave and rectilinear traveling property
like light, and practical use of the electromagnetic wave is
developed in the fields of communication, security, and
non-destructive inspection.
[0006] For example, in Japanese Patent Application Laid-Open No.
2013-19861, the photo device as an inspection object is irradiated
with the light to detect the emitted electromagnetic wave in the
terahertz region. The photocarriers (free electrons or holes)
excited by the irradiation of the inspection object with the light
is accelerated and moved by an internal electric field. Therefore,
the electromagnetic wave is emitted to the outside. Characteristics
of the photo device are inspected by detecting the emitted
electromagnetic wave.
[0007] Japanese Patent Application Laid-Open No. 2013-19861 also
discloses that a reverse bias voltage is applied to the photo
device in order to enhance an S/N ratio of an intensity of the
detected electromagnetic wave. The acceleration of the photocarrier
is increased by applying the reverse bias voltage, thereby
increasing the intensity of the emitted electromagnetic wave.
[0008] As to an alternative method for applying an external
electric field, Japanese Patent Application Laid-Open No.
2013-72843 proposes that the inspection object is irradiated with
the high-intensity electromagnetic wave to apply the reverse bias
voltage to a measurement place.
[0009] However, in the conventional technology, it is necessary to
provide a circuit or light source applying the reverse bias voltage
in order to improve the S/N ratio of the electromagnetic wave
intensity, which results in an increase of apparatus cost and a
troublesome work to optimize a condition.
SUMMARY OF THE INVENTION
[0010] The present invention is aimed at an inspection apparatus
that inspects an inspection object including an anode and a
cathode.
[0011] In accordance with one aspect of the present invention, an
inspection apparatus includes: a short-circuiting element that
electrically connects an anode and a cathode of an inspection
object to short-circuit the inspection object; an irradiation part
that irradiates the inspection object short-circuited by the
short-circuiting element with light; and a detection part that
detects an electromagnetic wave emitted from the inspection object
in response to the irradiation of the inspection object with the
light from the irradiation part.
[0012] The internal electric field can easily be enhanced in the
inspection object by sort-circuiting the anode and the cathode.
Therefore, because the intensity of the emitted electromagnetic
wave can be enhanced, the S/N ratio of the detected electromagnetic
wave can be improved.
[0013] Preferably the anode is a p-type semiconductor and the
cathode is an n-type semiconductor.
[0014] The internal electric field can easily be enhanced with
respect to the inspection object including the p-type semiconductor
and the n-type semiconductor.
[0015] Preferably the inspection object is a multi-junction type
solar cell formed by stacking plural solar cells having absorption
wavelength regions different from each other.
[0016] The intensity of the emitted electromagnetic wave can be
enhanced without applying the reverse bias voltage with respect to
the multi-junction type solar cell. Therefore, the breakage of the
solar cell can be constrained.
[0017] The present invention is aimed at an inspection method for
inspecting an inspection object including an anode and a
cathode.
[0018] In accordance with one aspect of the present invention, an
inspection method includes the steps of: (a) electrically
connecting the anode and the cathode to short-circuit the
inspection object; and (b) irradiating the inspection object
short-circuited in the step (a) with light to detect an
electromagnetic wave emitted from the inspection object in response
to the irradiation of the inspection object with the light.
[0019] Preferably the anode is a p-type semiconductor and the
cathode is an n-type semiconductor.
[0020] Preferably the inspection object is a multi-junction type
solar cell formed by stacking plural solar cells having absorption
wavelength regions different from each other.
[0021] Therefore, an object of the present invention is to provide
a technology of easily enhancing the intensity of the
electromagnetic wave emitted from the inspection object.
[0022] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0023] FIG. 1 is a schematic diagram illustrating a configuration
of an inspection apparatus according to a preferred embodiment;
[0024] FIG. 2 is a schematic diagram illustrating configurations of
an irradiation part, a detection part, and a delay unit that are
included in the inspection apparatus;
[0025] FIG. 3 is a schematic sectional view of a solar cell;
[0026] FIG. 4 is a view illustrating a time waveform of an
electromagnetic wave emitted from the solar cell in a short-circuit
state and a time waveform of an electromagnetic wave emitted from
the solar cell in an opened state;
[0027] FIG. 5 is a view illustrating an energy band of the solar
cell in the opened state;
[0028] FIG. 6 is a view illustrating an energy band of the solar
cell in the short-circuit state;
[0029] FIG. 7 is a flowchart illustrating an inspection example of
the solar cell;
[0030] FIG. 8 is a view illustrating an example of an
electromagnetic wave intensity distribution image;
[0031] FIG. 9 is a view illustrating an example of a spectral
distribution of the electromagnetic wave; and
[0032] FIG. 10 is a conceptual view illustrating a multi-junction
type solar cell.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Hereinafter, preferred embodiments of the present invention
will be described below with reference to the accompanying
drawings. In the drawings, for the sake of easy understanding, a
size of each unit or the number of units is exaggerated or
simplified as needed basis. The components of the preferred
embodiment are described only by way of example, but the present
invention is not limited to the preferred embodiment.
1. Preferred Embodiment
1.1. Configuration and Function
[0034] FIG. 1 is a schematic diagram illustrating a configuration
of an inspection apparatus 100 according to a preferred embodiment.
FIG. 2 is a schematic diagram illustrating configurations of an
irradiation part 12, a detection part 13, and a delay part 14 that
are included in the inspection apparatus 100.
[0035] The inspection apparatus 100 irradiates an inspection object
that is of a semiconductor device or a photo device with pulse
light, and detects an electromagnetic wave (for example, a
terahertz wave having frequencies of 0.1 THz to 30 THz) that is
emitted from the inspection object in response to the irradiation
of the inspection object with the pulse light, thereby inspecting
the inspection object.
[0036] As used herein, the semiconductor device means electronic
devices in which a transistor, an integrated circuit (IC or LSI), a
resistor, and a capacitor are made of semiconductor. The photo
device means electronic devices, such as a photodiode, image
sensors such as a CMOS sensor and a CCD sensor, a solar cell, and
an LED, in which a semiconductor photoelectric effect is used. The
surface of the inspection object is formed flat. Alternatively, the
surface of the inspection object may be formed into a curved
shape.
[0037] In the preferred embodiment, a solar cell 90 is inspected as
the inspection object by way of example. However, the semiconductor
device and the photo device can also be inspected.
[0038] As illustrated in FIGS. 1 and 2, the inspection apparatus
100 includes a stage 11, the irradiation part 12, the detection
part 13, the delay part 14, a stage moving mechanism 15, a control
part 16, a monitor 17, a manipulation and input part 18, and a
camera 19.
[0039] The solar cell 90 is held on the stage 11 by fixing means
(not illustrated). Examples of the fixing means include means in
which a clipping tool clipping a substrate is used, an adhesive
sheet, and a suction hole formed in a surface of the stage 11.
Alternatively, any fixing means may be used as long as the solar
cell 90 can be fixed. In the preferred embodiment, the solar cell
90 is held on the stage 11 such that the irradiation part 12 and
the detection part 13 are arranged on a side of a light receiving
surface (surface 90S) of the solar cell 90.
[0040] As illustrated in FIG. 2, the irradiation part 12 includes a
femtosecond laser 121. For example, the femtosecond laser 121 emits
pulse light (pulse light LP1) having a wavelength including visible
light regions of 360 nm (nanometer) to 1.5 .mu.m (micrometer).
Specifically, the femtosecond laser 121 emits the
linearly-polarized pulse light having a center wavelength of around
800 nm, periods of several kilohertz to several hundred megahertz,
and pulse widths of about 10 femtosecond to about 150 femtosecond.
Alternatively, the femtosecond laser 121 may emit the pulse light
having another wavelength region (for example, visible light
wavelength such as a blue wavelength (450 nm to 495 nm) and a green
wavelength (495 nm to 570 nm)).
[0041] The pulse light LP1 emitted from the femtosecond laser 121
is split into two by a beam splitter B1. Although not illustrated,
a light chopper performs several-kilohertz modulation to one of the
split pieces of pulse light (pulse light LP11). For example, an AOM
(Acousto-Optic Modulator) may be used as a modulation element. The
modulated pulse light LP11 is guided to the solar cell 90. The
other piece of pulse light (pulse light LP12) split by the beam
splitter B1 is guided to a detector 131 of the detection part 13
detecting the electromagnetic wave.
[0042] The irradiation part 12 irradiates the solar cell 90 with
the pulse light LP11 from the light receiving surface side. The
solar cell 90 is irradiated with the pulse light LP11 such that an
optical axis of the pulse light LP11 is obliquely incident to the
light receiving surface of the solar cell 90. In the first
preferred embodiment, an irradiation angle is set such that an
incident angle becomes 45 degrees. However, the incident angle is
not limited to 45 degrees, but the incident angle can be properly
changed within a range of 0 degree to 90 degrees.
[0043] FIG. 3 is a schematic sectional view of the solar cell 90.
For example, the solar cell 90 is constructed as a crystalline
silicon solar cell. The solar cell 90 has a stacked structure
including a plate-shape backside electrode 92 made of aluminum, a
p-type silicon layer 93, an n-type silicon layer 94, an
anti-reflection film 95, a lattice-shape light receiving surface
electrode 96, and a pn-junction 97 in the ascending order. The
anti-reflection film 95 is made of oxide silicon, nitride silicon,
or oxide titanium and the like.
[0044] In principal surfaces on both sides of the solar cell 90,
the principal surface on the side on which the light receiving
surface electrode 96 is provided constitutes the light receiving
surface. That is, the solar cell 90 is designed to suitably
generate power by receiving the light from the light receiving
surface side. A transparent electrode may be used as the light
receiving surface electrode 96.
[0045] The inspection apparatus 100 may be applied to the
inspection of a solar cell (such as an amorphous silicon solar
cell) other than the crystalline silicon solar cell. For the
amorphous silicon solar cell, generally energy gaps of 1.75 eV to
1.8 eV are larger than an energy gap of 1.2 eV of the crystalline
silicon solar cell. In such cases, the terahertz wave can well be
generated in the amorphous silicon solar cell by setting the
wavelength of the femtosecond laser 121 to, for example, 700 .mu.m
or less. The inspection apparatus 100 can also be applied to other
semiconductor solar cell (such as a CIGS solar cell and a GaAs
solar cell) with a similar way of thinking.
[0046] When a region in which an internal electric field of the
solar cell 90 exists is irradiated with the pulse light LP11 having
energy exceeding a bandgap, photocarriers (free electrons and
holes) are generated, and accelerated by the internal electric
field. Therefore, a pulse-shape current is generated, and an
electromagnetic wave is generated according to the pulse-shape
current. It is well known that the internal electric field is
generated in the pn-junction 97 or a Schottky junction.
[0047] As illustrated in FIG. 2, electromagnetic wave LT1 emitted
from the solar cell 90 is collected by parabolic mirrors M1 and M2.
More particularly, the parabolic mirrors M1 and M2 collect the
electromagnetic wave LT1 emitted on the side identical to the
surface 90S irradiated with the pulse light LP11. The collected
electromagnetic wave LT1 is incident to the detector 131.
[0048] The detector 131 is constructed with a photoconductive
switch (photoconductive antenna) to which the pulse light LP12 is
incident. For example, a dipole type photoconductive switch, a
bow-tie type photoconductive switch, and a spiral type
photoconductive switch are well known. When the detector 131 is
irradiated with the pulse light LP12 while the electromagnetic wave
LT1 is incident to the detector 131, the current is instantaneously
generated in the photoconductive switch according to an electric
field intensity of the electromagnetic wave LT1. The current
corresponding to the electric field intensity is converted into a
digital quantity through a lock-in amplifier, an I/V conversion
circuit, and an A/D conversion circuit (all of which are not
illustrated). Thus, the detection part 13 detects the electric
field intensity of the electromagnetic wave LT1 emitted from the
solar cell 90 in response to the irradiation of the solar cell 90
with the pulse light LP12.
[0049] Other elements such as a Schottky barrier diode may be used
as the detector 131. The Schottky barrier diode having small
polarization dependence is suitable for the detector 131.
Alternatively, a non-linear optical crystal may be used as the
detector 131.
[0050] The delay part 14 is provided on an optical path of the
pulse light LP12 from the beam splitter B1 to the detector 131. The
delay part 14 is an optical element that continuously changes an
arrival time the pulse light LP12 reaches the detector 131.
[0051] More particularly, the delay part 14 includes a delay stage
141 and a delay stage moving mechanism 143. The delay stage 141
includes a return mirror 10M that turns back the pulse light LP12
along an incident direction. The delay stage moving mechanism 143
translates the delay stage 141 along the incident direction of the
pulse light LP12 under the control of the control part 16. The
translation of the delay stage 141 continuously changes an optical
path length of the pulse light LP12 from the beam splitter B1 to
the detector 131.
[0052] The delay stage 141 changes a time difference between the
time the electromagnetic wave LT1 reaches the detector 131 and the
time the pulse light LP12 reaches the detector 131. The delay stage
141 changes the optical path length of the pulse light LP12, which
allows the detector 131 to delay the time (detection time or
sampling time) the electric field intensities of the
electromagnetic wave LT1 is detected.
[0053] The time the pulse light LP12 reaches the detector 131 can
be changed by another configuration different from the delay stage
141. Specifically, an electro-optical effect may be used. That is,
an electro-optical element in which a refractive index is changed
by changing an applied voltage may be used as the delay element.
For example, the electro-optical element disclosed in Japanese
Patent Application Laid-Open No. 2009-175127 may be used.
[0054] Alternatively, the optical path length of the pulse light
LP11 or the optical path length of the electromagnetic wave LT1
emitted from the solar cell 90 may be changed. In this case, a time
the electromagnetic wave LT1 reaches the detector 131 can be
shifted relative to the time the pulse light LP12 reaches the
detector 131. That is, the time the detector 131 detects the
electric field intensity of the electromagnetic wave LT1 can be
delayed.
[0055] The inspection apparatus 100 includes a short-circuiting
element 99 that short-circuits the solar cell 90. For example, the
short-circuiting element 99 is constructed with an electric wire.
One end of the short-circuiting element 99 is connected to the
light receiving surface electrode 96 attached to the n-type
semiconductor layer 94 (cathode), and the other end is connected to
the backside electrode 92 attached to the p-type semiconductor
layer 93 (anode). Thus, the short-circuiting element 99
electrically connects the cathode and anode of the solar cell 90 to
put the solar cell 90 into a short-circuit state.
[0056] FIG. 4 is a view illustrating a time waveform 41 of the
electromagnetic wave emitted from the solar cell 90 in the
short-circuit state and a time waveform 43 of the electromagnetic
wave emitted from the solar cell 90 in an opened state. In FIG. 4,
a horizontal axis indicates the time and a vertical axis indicates
the electromagnetic wave intensity.
[0057] As used herein, the "opened state" means a state in which
the backside electrode 92 and light receiving surface electrode 96
of the solar cell 90 are not electrically connected to each other.
As is clear from FIG. 4, an intensity of the time waveform 41 of
the electromagnetic wave LT1 emitted from the solar cell 90 in the
short-circuit state is larger than that of the time waveform 43 in
the opened state. A factor that increases the electric field
intensity of the electromagnetic wave LT1 emitted by the short
circuit will be described with reference to FIGS. 5 and 6.
[0058] FIG. 5 is a view illustrating an energy band of the solar
cell 90 in the opened state. FIG. 6 is a view illustrating the
energy band of the solar cell 90 in the short-circuit state. As
illustrated in FIG. 5, the optically-excited photocarriers (free
electrons 71 and holes 73) are drifted in the solar cell 90 in the
opened state. However, because the backside electrode 92 and the
light receiving surface electrode 96 are opened, drifted charges
are accumulated in the semiconductor. Therefore, as illustrated in
FIG. 5, photovoltaic power that weakens the internal electric field
of the pn-junction 97 is generated, and a Fermi level FL1 becomes a
state close to a forward bias. The intensity of the electromagnetic
wave LT1 emitted from solar cell 90 in response to the irradiation
of the solar cell 90 with the pulse light LP11 depends on intensity
of the internal electric field. Therefore, the electromagnetic wave
LT1 emitted from the solar cell 90 in the opened state in response
to the irradiation of the solar cell 90 with the pulse light LP11
decreases relatively by the decrease in internal electric
field.
[0059] On the other hand, as illustrated in FIG. 6, in the solar
cell 90 in the short-circuit state, the p-type semiconductor layer
93 is equal to the n-type semiconductor layer 94 in a potential,
and a Fermi level FL2 becomes flat. In the pn-junction 97 of the
solar cell 90 in the short-circuit state, the free electrons 71
generated by the irradiation flow to a negative electrode on the
side of the n-type semiconductor layer 94, and the holes 73
generated by the irradiation flow to a positive electrode on the
side of the p-type semiconductor layer 93. The charges are injected
into the other semiconductor via the short-circuiting element 99.
Then the charges are lost by recombination.
[0060] That is, in the short-circuit state, the photocarriers are
easily drifted because the charges generated during the opened
state are constrained from being accumulated. Therefore, it is
considered that the solar cell 90 is put into the short-circuit
state to be able to relatively enhance the intensity of the
electromagnetic wave LT1 emitted in response to the irradiation of
the solar cell 90 with the pulse light LP11.
[0061] Again, the configuration of the inspection apparatus 100
will further be described. The stage moving mechanism 15 is a
device that moves the stage 11 in a two-dimensional plane. For
example, the stage moving mechanism 15 is constructed with an X-Y
table or the like. The stage moving mechanism 15 moves the solar
cell 90 held by the stage 11 relative to the irradiation part 12.
In the inspection apparatus 100, the solar cell 90 can be moved to
any position in the two-dimensional plane by the stage moving
mechanism 15.
[0062] In the preferred embodiment, the stage moving mechanism 15
moves the stage 11 in the X-Y direction, which allows a required
inspection range on the solar cell 90 to be scanned with the pulse
light LP11. That is, the stage moving mechanism 15 constitutes the
scanning mechanism. Alternatively, the scanning of the inspection
range may be performed by changing the optical path of the pulse
light LP11 instead of moving the stage 11 with the stage moving
mechanism 15. Specifically, a galvano-mirror (not illustrated) is
provided, and the surface 90S of the solar cell 90 is scanned with
the pulse light LP11 in two directions perpendicular to the optical
axis of the pulse light LP11. A polygon mirror, a piezoelectric
mirror, or an acousto-optical element is considered to be used
instead of the galvano-mirror.
[0063] The control part 16 is constructed with a general computer
including a CPU, a ROM, and a RAM (all of which are not
illustrated). The control part 16 is connected to the femtosecond
laser 121, the detector 131, the delay stage moving mechanism 143,
and the stage moving mechanism 15 shown in FIG. 2. The control part
16 controls operations of these units, and receives data from these
units.
[0064] The control part 16 is connected to an image generation part
21, a time waveform restoration part 23, and a spectral analyzer 25
shown in FIG. 1. The image generation part 21, the time waveform
restoration part 23, and the spectral analyzer 25 may be a function
that is implemented by the operation of the CPU included in the
control part 16 according to a program (not illustrated), or be
implemented in a hardware manner by a dedicated circuit.
[0065] The image generation part 21 generates an electric field
intensity distribution image in which an electric field intensity
distribution of the electromagnetic wave LT1 emitted by the
irradiation of the inspection object range (a part or whole of the
solar cell 90) of the solar cell 90 with the pulse light LP11 is
visualized. In the electric field intensity distribution image, a
difference in electric field intensity is visually expressed by a
different color or a different pattern.
[0066] The time waveform restoration part 23 restores the time
waveform of the electromagnetic wave LT1 emitted from the solar
cell 90 based on the electric field intensity detected by the
detector 131. Specifically, the time the pulse light LP12 reaches
the detector 131 is changed by moving the delay stage 141, thereby
acquiring the electric field intensity of the electromagnetic wave
LT1 detected in each phase. The time waveform of the
electromagnetic wave LT1 is restored by plotting the acquired
electric field intensity on a time axis.
[0067] The spectral analyzer 25 performs a spectral analysis of the
solar cell 90 based on the restored time waveform of the
electromagnetic wave LT1. Particularly, the spectral analyzer 25
acquires an amplitude intensity spectrum concerning the frequency
by performing a Fourier transform of time waveform information.
[0068] The monitor 17 and the manipulation and input part 18 are
connected to the control part 16. The monitor 17 is a display
device such as a liquid crystal display, and displays various
pieces of image information to the operator. For example, the image
of the surface 90S of the solar cell 90 photographed by the camera
19, the electric field intensity distribution image generated by
the image generation part 21, the time waveform of the
electromagnetic wave LT1 restored by the time waveform restoration
part 23, and the spectral information acquired by the spectral
analyzer 25 are displayed on the monitor 17. A GUI (Graphical User
Interface) screen necessary to set an inspection condition (such as
an inspection range) is also displayed on the monitor 17.
[0069] The manipulation and input part 18 is constructed with
various input devices such as a mouse and a keyboard. The operator
can perform a predetermined manipulation input through the
manipulation and input part 18. When a touch panel is used as the
monitor 17, the monitor 17 may also act as the manipulation and
input part 18.
[0070] The control part 16 is connected to a storage (not
illustrated) in which various pieces of data are stored. The
storage is constructed with a portable medium (such as a magnetic
medium, an optical disk medium, and a semiconductor memory) in
addition to a fixed disk such as a hard disk. The control part 16
and the storage may be connected to each other through a
network.
1.2. Inspection of Solar Cell
[0071] FIG. 7 is a flowchart illustrating an inspection example of
the solar cell 90. Hereinafter, unless otherwise noted, it is
assumed that each operation of the inspection apparatus 100 is
performed under the control of the control part 16. It is assumed
that plural processes are concurrently performed depending on a
content of each process, or it is assumed that the order of plural
processes is properly changed depending on a content of each
process.
[0072] The solar cell 90 as the inspection target is placed on the
stage 11 (Step S11 in FIG. 7). At this point, as described above,
the solar cell 90 is set such that the light receiving surface
(that is, the principal surface on the side on which sunlight is
received in the use state of the solar cell 90) is irradiated with
the pulse light LP11.
[0073] When the solar cell 90 is placed on the stage 11, electrodes
of the short-circuiting element 99 are connected to the backside
electrode 92 and light receiving surface electrode 96 of the solar
cell 90. Therefore, the solar cell 90 is put into the short-circuit
state (Step S12 in FIG. 7).
[0074] When the solar cell 90 is put into the short-circuit state,
measurement of the electromagnetic wave is started (Step S13 in
FIG. 7). Particularly, the solar cell 90 is irradiated with the
pulse light LP11 emitted from the femtosecond laser, whereby the
electromagnetic wave LT1 emitted from the solar cell 90 is detected
by the detector 131.
[0075] Any detection time the detector 131 detects the
electromagnetic wave LT1 can previously be decided. For example, at
any typical point on the solar cell 90, the time waveform of the
emitted electromagnetic wave LT1 is restored, and the detection
time the electric field intensity of the electromagnetic wave LT1
is maximized may be set to the detection time in Step S13. The
decision of the detection time can enhance a possibility that the
electromagnetic wave LT1 emitted from each point in the inspection
object region of the solar cell 90 is detected with high intensity.
As described above, the setting of the detection time is performed
by adjusting the delay part 14.
[0076] When the measurement of the electromagnetic wave is started,
the stage 11 moves in the two-dimensional plane by driving the
stage moving mechanism 15. Therefore, the solar cell 90 is
two-dimensionally scanned with the pulse light LP11 (Step S14 in
FIG. 7).
[0077] Particularly, the solar cell 90 moves to a first direction
(main scanning direction) parallel to the surface 90S of the solar
cell 90, thereby scanning one end to the other end in the
inspection object region of the solar cell 90 with the pulse light
LP11 (main scanning). Then the solar cell 90 moves to a second
direction (sub-scanning direction), which is parallel to the
surface 90S of the solar cell 90 and orthogonal to the main
scanning direction, by a required pitch (sub-scanning). The solar
cell 90 moves in a direction opposite to the first direction to
perform the next main scanning. Thus, the two-dimensional scanning
of the inspection object region in the solar cell 90 is
two-dimensionally scanned by alternately performing the main
scanning and the sub-scanning.
[0078] When the electric field intensity of the electromagnetic
wave LT1 is acquired in each position at which the solar cell 90 is
irradiated with the pulse light LP11 in Step S14, the
electromagnetic wave intensity distribution image is generated by
the image generation part 21, and displayed on the monitor 17 (Step
S15 in FIG. 7).
[0079] FIG. 8 is a view illustrating an example of an
electromagnetic wave intensity distribution image i1. According to
the electromagnetic wave intensity distribution image i1, the
electric field intensity distribution in the solar cell 90 can
easily be understood. For example, the defective place of the solar
cell 90 can easily be identified based on the electric field
intensity distribution.
[0080] The inspection apparatus 100 can further analyze the portion
that is identified as the defective place in the solar cell 90.
Specifically, it is considered that a detailed inspection is
performed by restoring the time waveform of the electromagnetic
wave LT1 emitted from the portion concerned.
[0081] For example, the time waveform includes pieces of
information on the generation, movement, and recombination of the
photocarriers excited by the pulse light LP11. Therefore, the
analysis of the time change of the time waveform is quite effective
in analyzing the photocarrier dynamics.
[0082] FIG. 9 is a view illustrating an example of a spectral
distribution 61 of the electromagnetic wave LT1. The Fourier
transform of the time waveform is performed to acquire the spectral
distribution 61, which allows information on a physical property to
be analyzed in the inspection object portion. In FIG. 9, the
vertical axis indicates a spectral intensity and the horizontal
axis indicates the frequency.
[0083] The inspection based on the time waveform is not necessarily
performed after Step S15 (a process of generating and displaying
the electromagnetic wave intensity distribution image) shown in
FIG. 7. For example, the inspection based on the time waveform ay
be performed instead of Step S14 (two-dimensional scanning) shown
in FIG. 7.
[0084] As described above in the preferred embodiment, the
short-circuiting element 99 puts the solar cell 90 into the
short-circuit state, which allows the intensity of the emitted
electromagnetic wave LT1 to be enhanced compared with the solar
cell in the opened state. This enables an S/N ratio to be improved
in detecting the electromagnetic wave.
[0085] The short-circuiting element 99 can be constructed with a
simple electric wire. In the case that a reverse bias voltage is
applied to the solar cell 90, it is necessary to provide a power
supply in order to generate the high-intensity electromagnetic wave
LT1, which results in an increase of apparatus cost. Accordingly,
the inspection apparatus 100 of the preferred embodiment is
advantageous in cost compared with the conventional inspection
apparatus.
[0086] The solar cell 90 shown in FIG. 3 is a single-junction type
solar cell including one pn-junction 97. The inspection apparatus
100 can also be applied to an inspection of a multi-junction type
solar cell.
[0087] FIG. 10 is a conceptual view illustrating a multi-junction
type solar cell 90A. The solar cell 90A is a three-junction type
solar cell. Specifically, the solar cell 90A is constructed by
stacking three solar cells 9A, 9B, and 9C having absorption
wavelength regions different from one another in the ascending
order.
[0088] As used herein, the absorption wavelength region means a
wavelength region that is mainly absorbed in the solar cell, and
the absorption wavelength region can also be called a use
wavelength region. The plural solar cells 9A, 9B, and 9C do not
completely differ from one another in the absorption wavelength
region, but the absorption wavelength regions of the solar cells
9A, 9B, and 9C may be partially overlapped one another.
[0089] In the solar cells 9A, 9B, and 9C, similarly to the solar
cell 90, p-type semiconductor layers 93A, 93B, and 93C are joined
to n-type semiconductor layers 94A, 94B, and 94C to form
pn-junctions, respectively. Light receiving surface electrodes 96A
are attached to a top surface of the solar cell 9C constituting a
light receiving surface (surface 90SA) of the solar cell 90A, and a
backside electrode 92A is attached to a bottom surface of the solar
cell 9A constituting a back side of the solar cell 90A. The solar
cells 9A and 9B are electrically connected to each other, and the
solar cells 9B and 9C are electrically connected to each other.
[0090] In the multi-junction type solar cell 90A, the
short-circuiting element 99 puts the solar cell 90A into the
short-circuit state, which allows the higher-intensity
electromagnetic wave LT1 to be generated compared with the solar
cell 90A in the opened state. Compared with the single-junction
type solar cell 90, the multi-junction type solar cell 90A has a
higher possibility that the solar cell 90A is broken by the
application of the reverse bias voltage. For this reason, the
electromagnetic wave LT1 is particularly effectively measured while
the multi-junction type solar cell 90A is put into the
short-circuit state.
[0091] Although the detailed description is omitted, similarly to
the three-junction type solar cell 90A, the inspection can be
performed in the short-circuit state with respect to multi-junction
type solar cells such as a two-junction type solar cell or four or
more-junction type solar cell.
2. Modifications
[0092] In the preferred embodiment, as illustrated in FIG. 2, the
surface 90S of the solar cell 90 is obliquely irradiated with the
pulse light LP1, and the detector 131 detects the electromagnetic
wave LT1 emitted from the side of the surface 90S. Alternatively,
for example, the inspection apparatus 100 may have a configuration
in which the surface 90S of the solar cell 90 is perpendicularly
irradiated with the pulse light LP11 to detect the electromagnetic
wave LT1 emitted in the direction coaxial with the pulse light
LP11. When a transparent conductive film substrate (ITO) is used,
the electromagnetic wave LT1 is selectively reflected while the
pulse light LP11 is transmitted, and the optical path of the
electromagnetic wave LT1 can be changed.
[0093] Alternatively, the inspection apparatus 100 may have a
configuration in which the surface 90S of the solar cell 90 is
irradiated with the pulse light LP11 to detect the electromagnetic
wave LT1 emitted onto the back side of the solar cell 90.
[0094] In the preferred embodiment, the identical femtosecond laser
121 is used as the light source of the pulse light LP11 with which
the solar cell 90 is irradiated and the light source of the pulse
light LP12 incident to the detector 131. Therefore, the pulse light
LP11 is identical to the pulse light LP12 in a pulse period.
Alternatively, the pulse light LP11 and the pulse light LP12 may be
emitted from different femtosecond lasers having the identical
pulse period.
[0095] It is also conceivable that two variable wavelength lasers
having slightly different oscillation frequencies are used instead
of the femtosecond laser 121. Particularly, two laser beams emitted
from the variable wavelength lasers are overlapped with each other
using a coupler (not illustrated) formed by an optical fiber that
is of an optical waveguide, thereby generating an optical beat
signal corresponding to a difference between the frequencies. The
electromagnetic wave (terahertz wave) corresponding to the
frequency of the optical beat signal can be emitted by irradiating
the solar cell 90 with the optical beat signal. A
distributed-feedback (DFB) laser that substantially continuously
(for example, every 2 nm) changes the wavelength of the emitted
laser beam by temperature control can be used as a variable
wavelength laser.
[0096] In the preferred embodiment, as illustrated in FIG. 3, the
solar cell 90 in which the pn-junction 97 is formed is described by
way of example. Additionally, a solar cell in which an intrinsic
semiconductor layer is sandwiched between the p-type semiconductor
layer 93 and the n-type semiconductor layer 94, namely, a solar
cell in which what is called a pin-junction is formed can become
the inspection object of the inspection apparatus 100. Not the
pn-junction 97 but what is called a Schottky barrier diode in which
the p-type semiconductor or the n-type semiconductor and metal are
joined can become the inspection object of the inspection apparatus
100. In both the types, the short-circuiting element 99
electrically connects the cathode and the anode of the inspection
object to put the inspection object into the short-circuit state,
and the electromagnetic wave can be measured in the short-circuit
state.
[0097] While the invention has been shown and described in detail,
the foregoing description is in all aspects illustrative and not
restrictive. It is therefore understood that numerous modifications
and variations can be devised without departing from the scope of
the invention.
* * * * *